Political Novice Taps His Own Wealth in Bid for a Blue State That May Be Up for Grabs

CHICAGO—A private-equity investor is emerging as the top Republican in Illinois's race for governor, tapping his own wealth and the populist playbook of Democratic Gov. Pat Quinn, in a blue state that polls show is up for grabs.

Though he has never run for office before, Bruce Rauner leads a crowded field of GOP contenders vying to take on Mr. Quinn. The race is seen as one of the best chances for Republicans to unseat a Democrat as...